Grinders are widely used to grind up small quantities of material for further processing and analysis. A container acting as a mortar has a grinding surface in the interior of its base usually conical or rounded in shape for receiving the grinding material. A pestle which is received in the container has a similarly shaped grinding surface and a cap is sealing engaged with the pestle shaft and the top of the container. Often the pestle is made in two or more parts which requires an assembly step and more importantly introduces the opportunity for misalignment of the pestle shaft during assembly. This can result in misalignment of the grinding surfaces and poor grinding results. Another issue is the complexity of the sealing of the cap with the container. Typically the cap requires an intricate sealing structure at its periphery for sealingly engaging the container and another device at its center for sealingly engaging the pestle shaft. A further issue arises because a number of different sizes are needed. Offering grinders of a number of different sizes require not only a number of different size containers but a number of different pestles with a number of different matching sizes of grinding tips. Another problem encountered when the pestle tip is made of one solid piece is “sinking”. Sinking is the dimpling or concavity which occurs in thick molded parts where cooling causes shrinkage resulting in surface sinking. This is critical when it occurs in the grinding surface area of the tip. Presently attempts to prevent sinking require extra manufacturing steps including a water bath.